The present invention relates to a window shade, and more particularly to a window shade designed with dual blinds.
As shown in FIG. 1, a time-honored window blind of prior art has a relatively simple construction, which can be made easily at a low cost. However, it has the following defects that need to be addressed and improved.
(a) The blind made of a thin material can be made more compact after being drawn up together; nevertheless it does not obscure light effectively. PA1 (b) The blind made of a thin material is a poor heat insulator and is also lacking in soundproof quality. PA1 (c) The blind made of a thin material does not effectively obscure or prevent sight of movement of persons in the room at night. PA1 (d) The string holes arranged in the blind permit sunlight or light of other sources to permeate the blind and can be used improperly as peep holes.
A Y-shaped and pleated blind fabric impervious to light was proposed to overcome the shortcomings described above, as described by Judkins in PCT/US88/0091, in which FIG. 2 shows that each of ridges arranged on the same side of the blind fabric has a shoulder of a predetermined width extended outwardly therefrom. A hole is punched at the same position in each of shoulders to accommodate a string so as to enhance the imperviousness of the blind to light. However, such blind fabric is not a feasible substitute in terms of production cost and is still used on a trial basis.
Another solution to the problems mentioned above is a honeycomb blind, as exemplified in Colson U.S. Pat. Nos. 4,450,027 and 4,603,072; Masuda U.S. Pat. No. 3,164,507; Suominer U.S. Pat. Nos. 4,288,485 and 4,388,354; and Anderson U.S. Pat. No. 4,685,986. The honeycomb blind is a workable alternative. However, a costly investment in new production facilities is called for, because the existing production machinery and technology used to make blinds of the conventional types are no longer compatible with the production of a honeycomb blind. In addition, a honeycomb blind has an inherent drawback in itself that it can not be made compact after being rolled up.